The present invention relates to gas turbine engines and in particular to an assembly of rotating components that use single piece pilot rings for radial piloting of adjacent components and frictional contact for torque transmission between these components.
Rings have been used in gas turbine engines for many purposes. For example, Meininghaus, U.S. Pat. No. 2,356,605 uses rings 17 between adjacent turbine rims to increase bending stiffness.
FIG. 1, in Kington et al., U.S. Pat. No. 5,664,413 shows a single piece pilot ring 54 disposed between a back-to-back centrifugal compressor and radial turbine. The pilot ring 54 serves two functions referred to as a radial function and an axial function. The radial function is maintaining concentricity between the compressor rotor 35 and the turbine rotor 37. This requires the pilot ring 54 to maintain radial contact with both rotors during assembly of the engine and during operation. During operation of the engine, the radial growth due to thermal and/or centrifugal expansion of the turbine rotor is significantly greater than that of the compressor rotor. As a result, the pilot ring 54 must roll to accomplish the radial function. The axial function is transferring the axial load between the two rotors which requires that the axial ends of the ring remain parallel. As a consequence, the ring cannot roll freely as the turbine rotor thermally grows at a faster rate than the compressor rotor, requiring large radial interference fits between the pilot ring and the rotors. Some of the disadvantages associated with large interference fits are that they require a large temperature difference of the components during assembly, the ring can pop off the compressor rotor if assembly is not completed quickly, clocking of the turbine relative to the compressor to achieve balance and xe2x80x9crun outxe2x80x9d is difficult, and large stresses can be generated in the ring causing it to yield which in turn can result in high vibrations in the engine.
To overcome these disadvantages, Kington further discloses a dual pilot ring 80 for use between a back-to-back centrifugal compressor and radial turbine. The dual pilot ring uncouples the axial function from the radial function by providing an inner ring for radial piloting the compressor rotor and turbine rotor, and an outer ring for transmitting axial loads. The two rings are separated by a clearance gap. As a result, the inner ring is no longer constrained by axial loads and is free to roll as the two rotors thermally and/or centrifugally grow at different rates.
Referring to FIGS. 1A and 1B, a typical prior art friction drive piloting system includes a first component 1 having a lower lip 2 clamped up to a second component 3 having an upper lip 4. The components are radially piloted through the lips 2 and 4 and axially piloted through either the upper or lower axial facing surfaces 5, 6, 7, and 8. The torque transfer is primarily carried through these axial facing surfaces when the two components are clamped together represented by the arrows labeled with an xe2x80x9cFxe2x80x9d. Under operating conditions, the two components may grow radially at different rates due to thermal and centrifugal effects of the rotating components. These friction drive systems typically require large interference fits, represented by arrows 9, to maintain radial piloting under the varying conditions. These large interference fits make it difficult to assemble and disassemble the components. This piloting scheme has also been known to cause face distortion, see FIG. 1B, which can change the rotor unbalance and increase the engine vibrations.
Accordingly, there is a need for a turbine assembly of rotating components in a gas turbine engine that uses a single piece pilot ring for radial piloting and frictional contact for torque transmission.
An object of the present invention is to provide an assembly of rotating components that uses single piece pilot rings for radial piloting of the components and frictional contact between the faces of the assembled components for torque transmission between the components.
The present invention meets this objective by providing an assembly that includes a first rotatable component having a first lip with a first axial facing surface and a second rotatable component having a second lip with a second axial facing surface. The components are held together by an axial load so that the first and second axial surfaces are in frictional contact across a radial plane whereby torque is transmitted between the components. A pilot ring is mounted either above or below the radial contact plane to maintain the radial position of the two components. These and other objects, features and advantages of the present invention, are specifically set forth in, or will become apparent from, the following detailed description of a preferred embodiment of the invention then read in conjunction with the accompanying drawings.